The invention relates to actuators and zone valves for heating systems.
Zone valves are often utilized in hydronic heating and cooling systems. The zone valves isolate specific areas or "zones" of the system. Typically, each zone valve is controlled by a thermostat, which causes the valve to open and close to achieve desired temperature changes.
Conventional zone valves are typically actuated by either a heat motor or an electric motor. In valves with a heat motor as the actuator, an electrically heated element causes linear movement of an actuating element that, in turn, opens the valve. In valves with electric motors, the motor and associated gears move an arm within the valve. As the arm moves, a rubber plunger at its end moves away from a seat, allowing liquid to flow around the plunger. The arm is typically rotated through an angle of only 20.degree. to 30.degree., leaving the plunger in the path of the flowing liquid.
U.S. Pat. No. 5,131,623 describes a zone valve for a hydronic heating or cooling system in which a motor-driven actuator rotates a ball valve through about a 90.degree. rotation, between closed and opened positions. The motor rotates the valve from its normal position, which may be either open or closed, to the opposite position, e.g., if the valve is normally closed, from the closed to the open position. When the motor is de-energized, the valve is returned to its normal position by a tension spring so configured that it provides sufficient restoring torque to overcome the frictional torque of the ball valve. This type of actuator tends to fail after relatively few cycles, due to fatiguing of the tension spring.
Other zone valves provide restoring torque by mounting a torsional spring on a gear shaft that transmits torque from the motor at a reduced rotational speed, relative to the drive shaft of the motor. A large torsional spring carrying a high preload is required in order to produce adequate restoring torque to the gear shaft. Accordingly, these valves are also subject to failure due to spring fatigue.
Many spring return zone valves suffer from premature failure due to impact when the valve comes to a sudden stop upon returning to its normal position.